This invention allows the production of tapered straight and cantilevered structures that are optimized for the maximal nanodelivery of electromagnetic radiation and chemicals and for the maximal sensitivity in the nanosensing of ionic phenomena with high efficiency. These structures are generated so that they can simultaneously act as force sensors with excellent dynamic characteristics. Unlike previous attempts at obtaining such elements with chemical etching techniques our methodology is based solely on the application of glass pulling technologies with specific protocols that can minimize the subwavelength travel of light waves and can maximize the dynamic capabilities of these devices. Unlike the glass etching techniques these glass pulling technologies are universally, applicable to glass micropipettes and fibers. In addition optimal geometries of force sensing glass micropipettes are invented for the optimal delivery of chemicals in nanoguantities in a defined and in a nanometrically controlled fashion.
This invention is based on advances in near-field optics.
Near-field optics is the development of optical elements that can work in the near-field of an object that is to be interrogated by light. In essence, the objective is to develop optical elements that can illuminate, detect and/or enhance optical phenomena within a distance, from the object, that is considerably less than the dimensions of one wavelength. Conventional optical instruments all of which work in the far-field are based on lenses which critically depend on the wave nature of light. Thus, these elements are inherently limited to operation in the far-field with associated problems of diffraction that intrinsically limits resolution to approximately half the wavelength of light. Near-field optical elements not only overcome this diffraction limit of resolution but also relax the wavelength dependence of optical resolution. In its simplest implementation [A. Lewis, M. Isaacson, A. Hartoonian and A. Murray, Biophysical J. 41, 405a (1983); Ultramicroscopy 13, 227 (1984).] near-field optics involves transmitting light through a subwavelength aperture that is brought in close proximity to a surface. The sample or the aperture is then scanned in order to obtain an image or create a pattern with the subwavelength spot of light that emanates from this near-field optical element.
The method of choice that is used throughout the world today to produce near-field optical elements was developed by Lewis et al. [U.S. Pat. No. 4,917,462]. The essence of the methodology of Lewis et al was to use heating, tension and pulling with microprocessor control to produce tapered glass structures that were subsequently coated with metal to form a subwavelength aperture. This was a simple, cheap and reliable method of producing these subwavelength optical elements. Nonetheless, these elements were produced without much regard to the geometry of the subwavelength tip in terms of reducing the subwavelength region through which the light wave traversed. It is important to realize that the technology in the Lewis et al patent was a general methodology for producing these subwavelength tips through which subwavelength points of light could be produced. This generality can be seen by the fact that the same technology could be used to produce tapered optical elements made out of glass capillaries [A. Harootunian, E. Betzig, M. S. Isaacson and A. Lewis, Appl. Phys. Lett. 49, 674 (1986)] or glass fibers [Betzig E., Trautman J. K., Harris T. D., Weiner J. S. and Kostelak R. L., Science 251, 1468 (1991)]. All of these structures, however, had less than optimized geometries at the tip and thus there were significant evanescent losses that resulted from the transmission of the electromagnetic radiation through the tip.
The first attempts at resolving this problem were made by workers who realized that geometries at the tip that were closer to what would be optimal for high transmission of the light wave through the subwavelength region could be approached with chemical etching of glass fibers [Ohtsu, M., S. Juang, T. Pangaribuan and M. Kozuma, Proceesing of NFO-1, 131-139 (1993); Jiang, S., Ohsawa, H., Yamada, K., Pangaribuan, T., Ohtsu, M., Imai, K., and Ikai, A., Jpn. J. Appl. Phys. 31, 2282 (1992)] without any previous tapering. Such structures had the potential to generate high throughputs if the coating of these structures could be effectively performed. The coating, however, was problematic since the etching technology resulted in damaged surfaces that were difficult to impossible to coat successfully. In addition, the angle required for coating such an etched structure was not compatible with the geometry of such untapered etched fibers. Furthermore, the geometry of such untapered elements (see FIG. 1) perturbed significantly the ability of such elements to track rough surfaces. Finally, the untapered nature of these elements made the glass leading to the subwavelength tip very stiff and this crucially reduced the ability of such tips to monitor surface forces. It was this sensitivity of the tapered tips to surface forces [Shalom S., Lieberman K. Lewis A and Cohen S. R., Rev. Sci. Instrm. 63, 4061 (1992)] that allowed the resolution of one of the principle problems of near-field optics which was the ability to bring such a subwavelength tip close to a surface that was to be interrogated. Also none of the etching methodologies could be applied to tapered micropipette structures whereas the pulling technology is applicable to both tapered micropipettes and optical fibers.
In view of all of these factors it would be best if the standard tapering methodology could be extended to produce a high throughput tip that would also be capable of effectively sensing surface forces.
This invention uses pulling technologies as applied to glass tubes to generate without any chemical etching a profile that is ideal to produce a high transmission subwavelength optical aperture with very good atomic force sensing capabilities. The same pulling technology with small amendations can be used to optimize similar structures that can combine force sensing capabilities with such applications as the nanodelivery of materials to surfaces.